Generic Kernels pertain mostly to natural bodies and are independant of any particular mission. Generic kernels contain information about how each planet rotates, what its dimensions are, how much mass it has etc.

NAIF has an entire area that hosts Generic Kernels.

For an explanation:
https://naif.jpl.nasa.gov/naif/data_generic.html

The actual download location:
https://naif.jpl.nasa.gov/pub/naif/generic_kernels/